visionmedia/express — pull request #1072 by brianloveswords (2012-04-10 17:23:31+00:00)
Title: The guide says that `res.contentType` can accept literal types. This makes that true.

I mentioned in the comments for #1047 that this will break code that does `res.contentType('path/foo.blagh')` with the expectation that they will get the fallback type `application/octet-stream` but I think that's an acceptable tradeoff.